What should i do next...

[goosemanhnt4fud]

I have an 83 Mercury 70hp outboard on the boat...

Here is my problem and things I have done so far:

The problem is that it will idle all day long but when I give it full throttle, it will plane out and run for 4 or 5 seconds on plane then sputter and die then as soon as the boat settles I can fire it up right away and it'll run again, When it is up on plane it seems fine and sounds really good, then it seems like the fuel is being shut off???

I have replaced the diaphram in the fuel pump, the filter in between the fuel tank and the motor, the bulb in the fuel line used for priming and the spark plugs and have done a compression test and all three cylinders were at 119...

I am looking for another direction to go...carbs need to be cleaned, maybe the floats?

If anyone can help me out and has any suggestions they will greatly be appreciated. Thanks so much and God Bless!!

 

[milehighboater]

Re: What should i do next...

Partially clogged vent tube?

 

[goosemanhnt4fud]

Re: What should i do next...

i will check/replace them today...thanks for the idea..

 

[ajgraz]

Re: What should i do next...

Welcome to hell...which I define as mid-70's to late 80's Mercury 3 cyl.

Some ideas:

1) check out this thread:
http://forums.iboats.com/showthread.php?t=398522

2) Does the bulb get soft when it sputters out? This may help ID whether it's a fuel delivery or a spark issue

3) Have you done any checks on ignition components? Perhaps the high-speed windings on the stator are going bad

 

[goosemanhnt4fud]

Re: What should i do next...

I checked out the thread and it sounds exactly like what I'm having with my motor..
yes.. the bulb gets soft.. I'm curious, if there are vacuum lines that take over the priming process once the motor fires and continues to run...
havent done anything ingnition related besides changing the spark plugs.

The thread is exactly the problem I'm having, but it sounds like I'm just getting started...

 

[ajgraz]

Re: What should i do next...

I checked out the thread and it sounds exactly like what I'm having with my motor..
yes.. the bulb gets soft.. I'm curious, if there are vacuum lines that take over the priming process once the motor fires and continues to run...
havent done anything ingnition related besides changing the spark plugs.

The thread is exactly the problem I'm having, but it sounds like I'm just getting started...

On these motors the fuel is pumped solely by a diaphragm in the fuel pump, and the diaphragm is oscillated by a port into the exhaust stream from the 3rd (bottom) cylinder. Check valves in the pump keep the fuel flowing one way, kinda like the chambers in your heart.

In the linked thread, there is mention of a kit (and also individual part numbers) for diaphragm and fuel pump check valves. I'd start there.
(Please verify first what p/n's you'd need for your serial number/year)

Next step might be carb rebuild/cleanup and new fuel filter if they've not been done in awhile.

BTW, is this something that's come on gradually, or all of a sudden?

 

[goosemanhnt4fud]

Re: What should i do next...

Yeah I have checked out the fuel filter and replaced it and replaced the diaphram in the pump, I was told the check valves rarely go out,( the guy didn't have any on hand) so I just got the diaphram.

I have had the boat/motor, for 3 years now, my grangfather used to own it, he said he had to put $1500 in it for the upper end..? Don't exactly know what was worked on. The first year there wasn't any problems, then last year every once in a while, in would sputter when I would give it full throttle, like a hesitation and then it was fine, then this year it has gotten wayyy worse, so now I'm at a point of repairing/learning.

The carbs haven't been done since I have got the boat, it is stored outside in the winter and this last year was the first time I winterized it... didn't knw any better the years past...

Thanks for all the help though, everyone is great on here, so helpful.

 

[crazymac-680]

Re: What should i do next...

You'll be glad to know that this isn't going to cost you a penny to fix. Before fuel reaches your float chamber they first have to pass through another chamber with a filter inside it. These are all clogged up with a white waxy stuff. While at idle the fuel is trickling through the filter and filling the float chamber. When you then gun it. The fuel cant get through the filter fast enough to replenish the float chamber and you splutter and stall unless you come off the gas back to idle.
It can be quite awkward to get to but an easy fix once you have made the space to work. The filters chamber has a gasket. I replaced my gasket with the cover from a yellow pages.
You might as well give the float chamber a clean too. Just use carb cleaner or white spirits would do the job too.
Good luck get stuck in and she will be performing like a champ again in no time

 

[goosemanhnt4fud]

Re: What should i do next...

Cool, thanks Crazymac...I will definently check that out also...

 

[goosemanhnt4fud]

Re: What should i do next...UPDATE...UPDATE

Re: What should i do next...UPDATE...UPDATE

ok...I have change all fuel lines, vent lines, replaced zip ties with hose claps, tightened vent fittings, took the carbs off and checked for the filter inside of them...I couldn't find them, is there a diagram that someone has that shows the filters' location...I took the bowls off the carbs and checked the float and took out the small "pin" that I believe prevents the flow of fuel coming into the bowl when the bowl is already full, the bowls looked really clean and so did the rest of the carb orfices... I put everything back together and took it to the lake and it continues to do the same.

I may need to find the location of the filters in the carb that Crazymac was talking about.

I was also thinking of bypassing the fuel pump itself and manually pumping fuel into the bowls in the carbs and seeing if it continues to run at WOT or continues to bog down...

Dont know what's next...any ideas??? Thanks in advance

 

[j_martin]

Re: What should i do next...

If it were mine, I would find a way to put a fuel pressure gauge on the line to the carbs, then study it when the problem occurs to see if it is actually a fuel delivery problem. If pressure stays up, it's in the carbs. If it doesn't, then troubleshoot that.

I found a fuel problem one time that turned out to be the owner had replaced the old stiff pulse line to the fuel pump with tygon. It needs a stiff line.

Oh, and drop the other thread. It's ridiculous to expect people to chase all over to track the progress of a thread and then help you. I'm giving you my time to start with, please don't waste it.

hope it helps
John

 

[coolguy147]

Re: What should i do next...

if you fix the fuel problem and other problems are fixed and yet it still does it mabye the low speed needles need to be backed out a little bit? 1/8 to 1/4 turns out from current settings. or does this motor not have that?

seems to me that your bogging down when you floor the motor. what happens if you ease it up to speed? does it still bog down? if so i would look into a fuel problem.

maybe a link and sync would help?

 

[goosemanhnt4fud]

Re: What should i do next...

I will check them again, I think I know where the screen is that crazymac was talking about is.

I will call up some places to see if I could borrow a fuel pressure gauge and check that out, I did check the Clymers manual, it says at idle I should have 2 psi and at full throttle it should be at least 2 psi.

Any one ever bypass a pump and manually pump fuel into the carbs?

 

[goosemanhnt4fud]

Re: What should i do next...

I will check them again, I think I know where the screen is that crazymac was talking about is.

I will call up some places to see if I could borrow a fuel pressure gauge and check that out, I did check the Clymers manual, it says at idle I should have 2 psi and at full throttle it should be at least 2 psi.

Any one ever bypass a pump and manually pump fuel into the carbs?

Hey J_martin, my bad about the other thread....newbie mistake..

 

[j_martin]

Re: What should i do next...

I will check them again, I think I know where the screen is that crazymac was talking about is.

I will call up some places to see if I could borrow a fuel pressure gauge and check that out, I did check the Clymers manual, it says at idle I should have 2 psi and at full throttle it should be at least 2 psi.

Any one ever bypass a pump and manually pump fuel into the carbs?

Hey J_martin, my bad about the other thread....newbie mistake..

No problem. You just got a dose of crust.

The pump has a diaphragm and 2 check valves in it. When you pump up the primer bulb, you push fuel right through the pump. You can easily get 10 lbs fuel pressure with just the squeeze bulb. You need about 2 to run the engine.

If, when it's bogging you squeeze the primer bulb and it recovers, the fuel pump is probably bad. It's normal for the primer bulb to go a little soft. It is in a suction line after all. It is not normal for it to collapse.

Another thing to look for is air in the suction line. You find that by installing a short length of clear hose between the primer and the engine and looking at it when it's running.

Sometimes there's more than one thing wrong. When I got my XR4 it bogged at WOT, and I shot no less than 7 bugs out of it before it was completely good.

hope it helps
john

 

[ajgraz]

Re: What should i do next...

Any one ever bypass a pump and manually pump fuel into the carbs?

On land, I've put the fuel tank up on a ladder a few feet above the motor; once fuel gets primed from the squeeze bulb it will keep flowing even if the pump's not working.

How you'd do that safely on the water, I dunno.

 

[j_martin]

Re: What should i do next...

On land, I've put the fuel tank up on a ladder a few feet above the motor; once fuel gets primed from the squeeze bulb it will keep flowing even if the pump's not working.

How you'd do that safely on the water, I dunno.

You wouldn't. You'd have the first mate squeeze the primer bulb repeatedly to pump fuel.

 

[crazymac-680]

Re: What should i do next...

Hope you got on ok Goosehunt. Did you find the screen/filter just above the floats? Was it clogged atall?
www.ribsmarineparts.co.uk is a cracking site with exploded diagrams of all the parts and engines.
Dan